Polyimide resins have excellent heat resistance so that they are widely used in the field of semi-conductor devices, etc. Polyimide resins are particularly used as an interlayer insulating film, and a surface protection film (buffer coating) which is provided between a sealant and a semi-conductor chip.
Here, the surface protection film is a film which prevents an aluminum thin film circuit and an oxidized film prepared in the previous step from damage during work of the post steps, or from occurrence of cracks due to the difference in the thermal expansion coefficient between a sealant and silicon after mounting a semi-conductor chip. In particular, the surface protection film formed of a polyimide resin attracts attention because of its protective performance against radiation due to high α-ray stopping power, in addition that it protects chips from external damages as mentioned above. Further, polyimide resins attract attention as a tool capable of being simply and assuredly patterned.
Recently, in order to shorten the process for production of a semi-conductor, photo-sensitive polyimides are becoming mainstream from which a relief pattern can be easily formed by a method of adding a compound having a photo-sensitive group to acidic functional groups of a polyimide precursor or mixing the compound to the polyimide precursor to give photo-sensitivity to the polyimide resin, followed by coating, light exposure and development (for example, JP-A-S54-109828 and JP-A-H04-204945).
Recently, from the viewpoint of material costs or environmental protection, there is an increasing demand for development using an alkaline aqueous solution. In this context, a photo-sensitive resin using a polybenzoxazole precursor having an acidic functional group as the base resin or the like are now proposed for an interlayer insulating film or a surface protection film (buffer coating) (for example, JP-B-H01-40862).
However, in the conventional polyimide resins and polybenzoxazole resins, there is a problem that when a relief pattern formed after development is subjected to the final heating step, the film melts so that the size of an opening pattern becomes smaller or the opening pattern disappears (hereinafter referred to as “melt”). This phenomenon occurs because a polyimide precursor or a polybenzoxazole precursor is heated at the final heating step at a temperature higher than the glass transition point thereof.
Namely, in the case where, for example, a polyimide precursor vanish or a polybenzoxazole precursor vanish is applied on a substrate, a relief pattern is formed and finally heated, dehydration ring closure reaction of the precursor is in progress during stepwise rising temperature at the final heating step, so that when the resin film is heated at a temperature higher than the glass transition point, melt of the relief pattern occurs. As a result, various problems such as no desired relief pattern being obtained have been taken place.
As a solution for the above-mentioned problems, a method wherein a cross-linking component is added to a polyimide precursor vanish or a polybenzoxazole precursor vanish is proposed (JP-A-2007-16214). However, by this method, the cross-linking component added may sublime at the time of heating. Further, when heated at a temperature higher than the final heating step at a step after the final heating step, a gas component generates due to decomposition of the cross-linking component. The gas component may cause various problems such as contamination of the metal surface of the opening, crack occurrence of the sealant and breaking of wirings.
In order to improve adhesiveness between the insulating film or the surface protection film and the substrate on which this films are formed, which is made of silicon, various metals, or the like at the time of forming a relief pattern and after the final heating step, an organic silicon compound is used (JP-A-2000-187321, JP-A-2006-071663, etc.). However, these techniques disclosed in these references are not techniques capable of dissolving the problems other than improvement of adhesiveness, such as the melt of the relief pattern.